CSLB C-8 Concrete (Trade Exam) — All Questions

Below what oxygen percentage is an atmosphere in an excavation considered oxygen deficient?

• a.19.5 percent✓
• b.10 percent
• c.21 percent
• d.16 percent

Title 8 treats atmospheres with less than 19.5 percent oxygen as deficient. 10 and 16 percent are far below the trigger and would let workers enter too late, while 21 percent is ordinary air.Cal. Code Regs. tit. 8, §1541

Water is steadily accumulating in a footing trench. Under Title 8, may employees work in it?

• a.Yes, provided the water looks clear and has no odor
• b.Yes, provided everyone on the crew wears rubber boots
• c.Yes, as long as the water is less than 12 inches deep
• d.Not without adequate precautions against water hazards✓

Employees may not work in excavations with accumulated or accumulating water without adequate precautions. Shallow depth, boots, and clear water do not remove the cave-in and drowning hazards.Cal. Code Regs. tit. 8, §1541

A backhoe is swinging a bucket of spoil over the edge of a trench. Where may employees stand?

• a.Under it, if they wear hard hats
• b.Under it, if the operator waves them in
• c.Never underneath the load✓
• d.Under it, if the load is small

No employee may be underneath loads handled by lifting or digging equipment. A hard hat, a signal, and a small load do not make the position safe.Cal. Code Regs. tit. 8, §1541

A trench will run along a sidewalk. May the sidewalk be undermined?

• a.Yes, because concrete flatwork can bridge any trench
• b.Yes, whenever the trench is shallower than 5 feet
• c.Not unless a support system or other protection is used✓
• d.Yes, whenever the sidewalk contains reinforcing steel

Sidewalks, pavements and appurtenant structures must not be undermined unless support or other protection prevents collapse. Slabs do not reliably span a void, trench depth under 5 feet is not an exception, and rebar does not carry a slab over open ground.Cal. Code Regs. tit. 8, §1541

A 6-ft-deep excavation in Type B soil will be sloped under Appendix B. How far back must each side lay back horizontally from the bottom edge?

• a.4.5 feet
• b.9 feet
• c.12 feet
• d.6 feet✓

Type B soil is sloped at 1:1 (45 degrees), so 6 ft deep means 6 ft back. 4.5 ft is the 3/4:1 slope for Type A, 9 ft is the 1 1/2:1 slope for Type C, and 12 ft would be a 2:1 slope that the table does not use.Cal. Code Regs. tit. 8, §1541.1, App. B

In Title 8, which description fits a trench?

• a.An open excavation that is wider across than it is deep
• b.A narrow cut deeper than wide, at most 15 ft at the bottom✓
• c.Any hole that was dug only with hand tools and a shovel
• d.Any open excavation more than 4 feet deep, however wide

A trench is generally deeper than it is wide, and its width measured at the bottom is not greater than 15 ft. A depth of 4 feet is a different threshold, an excavation wider than deep is not a trench, and the digging method is irrelevant.Cal. Code Regs. tit. 8, §1540

On a Caltrans job, how should the survey's control stakes be checked?

• a.Check only the stake at the first footing to be formed
• b.Spot-check the stakes at each location rather than resurvey✓
• c.Redo the entire survey from scratch before forms go up
• d.Accept them without checking, since the engineer set them

Control stakes carry location and elevation for all the work, so each location is spot-checked rather than the survey being recreated. Trusting them blind or checking just one risks building off a wrong stake, and a full re-survey is not needed.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 2

Which part of a forming system touches the concrete and gives it its surface texture?

• a.The wall studs
• b.The sheathing✓
• c.The horizontal walers
• d.The diagonal kickers

Sheathing is the form material in direct contact with the concrete, so it carries its texture. Studs back the sheathing, walers support the studs, and kickers are diagonal braces that keep forms plumb.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 3

Why are form studs spaced as they are?

• a.To give the snap ties something to hook onto
• b.To let the panels be stripped and reused
• c.To keep the whole wall form standing plumb
• d.To limit how far the sheathing bows between them✓

Studs are spaced to limit how far the sheathing bows between them under the concrete's pressure. Ties resist spreading, kickers keep forms plumb, and reuse depends on materials and handling, not stud spacing.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 3

What is the smallest triangular fillet Caltrans requires on exposed sharp edges of formed concrete?

• a.1/2 by 1/2 inch
• b.1 1/2 by 1 1/2 inch
• c.1/4 by 1/4 inch
• d.3/4 by 3/4 inch✓

Exposed edges get fillets not less than 3/4 by 3/4 inch to produce smooth, straight chamfers. 1/4 and 1/2 inch are below the minimum, and 1 1/2 inch is larger than required.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 3

Which method of holding forms in position is not permitted on a Caltrans job?

• a.He-bolt form ties
• b.Twisted wire loops✓
• c.Taper ties with rods
• d.Snap ties with wedges

Twisted wire loops are not permitted for holding forms. Snap ties, he-bolts and taper ties are all recognized tensile form ties that prevent the forms from spreading.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 3

Wood spreaders keep the faces of a wall form the correct distance apart. What must happen to them?

• a.They are cut off flush after the forms are stripped
• b.They are oiled and then left in place as sleeves
• c.They stay in the wall as extra permanent ties
• d.They must be pulled out during the pour✓

Wood spreaders cannot stay in the concrete and must come out as concrete rises. Leaving them, cutting them flush later, or treating them as sleeves all leave wood embedded in the wall.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 3

Why must forms be mortar-tight?

• a.A sealed form keeps the panels from floating up
• b.Standing water is needed in the form for curing
• c.Leaking grout means more finishing afterward✓
• d.It keeps the form ties from rusting in the wall

Grout leakage from forms that are not mortar tight increases the finishing required and can leave defects such as rock pockets. Curing water, floating panels, and tie rust are not the reason for tight joints.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 3

What do clean-out openings in formwork allow?

• a.Pumping water out of the form after the pour
• b.Inspection and debris removal✓
• c.Releasing air that the vibrator has trapped
• d.Placing concrete from the bottom of the form up

Clean-out openings let the crew inspect and remove debris before concrete goes in. They are not pump ports or placing points, and trapped air is dealt with by vibration, not by these openings.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)

Under the federal guide specification, when are adjustments to formwork not allowed?

• a.After release agent has been applied to the forms
• b.After the first truck arrives at the site
• c.After the rebar has been inspected and accepted
• d.After the concrete has reached initial setting✓

Formwork must not be adjusted once concrete has reached initial setting, because it would disturb the setting concrete. Inspected rebar, a truck's arrival, and release agent do not set that limit.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)

Under Title 8, when may form release oil be applied to horizontal formwork?

• a.After all of the reinforcing steel is tied
• b.Before any nailing starts, to protect the lumber
• c.After the carpentry on the form is finished✓
• d.At any time, if workers wear slip-resistant boots

Oil is not applied to horizontal forms until the carpentry is finished, so workers are not walking and nailing on slick surfaces. Oiling before nailing creates that hazard, tying steel is not the trigger, and boots do not replace the rule.Cal. Code Regs. tit. 8, §1713

A rectangular layout is 24 ft by 32 ft. If it is square, how long should each diagonal measure?

• a.45 feet
• b.40 feet✓
• c.56 feet
• d.28 feet

The diagonal is √(24² + 32²) = √1,600 = 40 ft, and equal diagonals show the corners are square. 56 adds the two sides, 28 averages them, and 45 is not the result of the right-triangle relationship.Field layout practice (right-triangle check)

A benchmark is 98.40 ft. The backsight reading on it is 3.25 ft, and the rod then reads 6.10 ft on a grade stake. What is the elevation at the stake?

• a.95.55 feet✓
• b.89.05 feet
• c.92.30 feet
• d.107.75 feet

Instrument height = 98.40 + 3.25 = 101.65 ft; stake elevation = 101.65 − 6.10 = 95.55 ft. 107.75 adds the second reading, 92.30 ignores the backsight, and 89.05 subtracts both readings from the benchmark.Field layout practice (differential leveling)

The federal guide specification lists polyethylene vapor retarder sheeting (ASTM E1745) with what minimum thickness as its base option?

• a.10 mil✓
• b.30 mil
• c.3 mil
• d.6 mil

The specification lists a minimum of 10 mil, with 15 mil as a heavier alternative. 3 and 6 mil are thinner than that base option (6 mil appears in a local Los Angeles note, not this specification), and 30 mil is not the stated minimum.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)

What can water trapped inside a pavement structure lead to?

• a.Subgrade pumping and weaker subgrade and base✓
• b.Higher air content in the delivered mix
• c.Faster early strength gain in the slab above
• d.Less drying shrinkage cracking in the slab

Trapped water leads to subgrade pumping and reduced subgrade and base strength, which is why drainage is designed in. Water does not speed strength gain, change air content, or reduce cracking.IMCP Manual for Concrete Pavement, 2nd ed. (FHWA/CP Tech Center, 2019)

Cement-treated permeable base is being placed over slotted pipe drains. What must be prevented?

• a.Water entering the slotted pipe
• b.Cement paste plugging the drain openings✓
• c.Any compaction of the base layer
• d.Contact between the base and the subgrade

Cement paste must not plug the drain openings, since that would defeat the drain. Water entering the pipe is its job, the base is compacted as specified, and contact with the subgrade is normal.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 6

What should a waterstop form in each joint where it is installed?

• a.A rigid expansion plate
• b.A rough bond breaker
• c.An open drainage gap
• d.A continuous diaphragm✓

Waterstops are installed to form a continuous diaphragm across the joint, which is why splices are kept to a minimum. A bond breaker, open gap, or rigid plate would not block water.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)

In designing drainage for a pavement, why are grade lines set high and side ditches made deep where possible?

• a.To reduce the quantity of concrete in the pavement
• b.To speed up the strength gain of the slab concrete
• c.To let the engineers make the base layer thinner
• d.To lengthen the gap from water table to subgrade✓

A higher grade and deeper ditches lengthen the distance from the water table to the prepared subgrade, keeping it drier. The base is not made thinner, curing speed is unaffected, and concrete quantity is not the aim.IMCP Manual for Concrete Pavement, 2nd ed. (FHWA/CP Tech Center, 2019)

Under the Los Angeles general notes for single-family dwellings, what must a concrete floor slab on grade be placed on?

• a.A 4-inch fill of coarse aggregate or a moisture barrier✓
• b.Bare compacted native soil with no fill or membrane
• c.A 12-inch bed of fine sand with no membrane under it
• d.A 2-inch bed of damp sand with no membrane at all

The note calls for a 4-inch fill of coarse aggregate or a moisture barrier membrane under floor slabs on grade. A thin sand bed, bare soil, and a deep bed of fine sand are not what the note says.LADBS Information Bulletin P/GI 2026-022 (general notes, single-family dwelling)

What lap length does Caltrans use for uncoated Grade 60 #9, #10 and #11 bars?

• a.45 times the bar diameter
• b.100 times the bar diameter
• c.30 times the bar diameter
• d.60 times the bar diameter✓

Nos. 9, 10 and 11 bars lap at 60 diameters, while #8 and smaller lap at 45. 30 diameters is too short, and 100 is longer than any rule given.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 4

Which reinforcement may not be lap spliced under Caltrans guidance?

• a.Small #3 and #4 bars in walls
• b.Any bars placed in a footing
• c.#14 and #18 bars, and all hoops✓
• d.Any bars larger than a #6 bar

Lap splicing is not allowed for #14 and #18 bars or for any hoops. Small bars are routinely lapped, footing bars can be lapped, and bars above #6 (up to #11) are lapped by the diameter rules.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 4

On reinforcing drawings, what does the clear distance between bars measure?

• a.The distance from the center of a bar to the form face
• b.The distance from center to center of adjacent bars
• c.The gap between the outer surfaces of two adjacent bars✓
• d.The length of a bar measured between its end bends

Clear distance is surface to surface, unlike center-to-center spacing, which measures between bar centers. Center-to-form measures something else, and bar length between bends is a detailing dimension.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 4

What are the "dobies" used under rebar on Caltrans jobs?

• a.Aluminum clips on the form
• b.Wood blocks cut to size
• c.Precast mortar blocks✓
• d.Plastic wheel-type chairs

Dobies are precast mortar blocks and are the most common spacer. Caltrans does not allow aluminum, plastic, or wood spacers and supports.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 4

How can an inspector check that reinforcement is tied firmly enough to stay in position?

• a.Try to move it out of position by hand✓
• b.Weigh a sample of the tied bars
• c.Pull each tie wire with pliers
• d.Count the tie wires per square foot

Not every intersection needs a tie, but the bars must stay put, and a hand check shows whether they do. Counting ties, weighing bars, and pulling wires do not test whether the mat holds position.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 4

What kind of tie wire goes on bars that carry a factory-applied protective coating?

• a.Galvanized wire, to prevent rust
• b.Epoxy-coated or plastic-coated wire✓
• c.Bare black wire, for the best bond
• d.Copper wire, for conductivity

Epoxy-coated bars are tied with non-conductive wire such as epoxy-coated or plastic-coated wire. Bare or galvanized wire can damage the coating or set up corrosion, and conductivity is something to avoid, not seek.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 4

Under the federal guide specification, which condition is cause to reject reinforcing bars?

• a.A grade mark rolled into the bar's surface
• b.Bends or kinks not shown on the drawings✓
• c.Ends that were cut square at the mill
• d.Bars that arrive bundled and tied with wire

Bars with bends or kinks not on the drawings or approved shop drawings are rejected, as are bars with reduced cross section. A grade mark, delivery bundles, and square-cut ends are normal.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)

What is an example of a benchmark inspection of reinforcement?

• a.Measuring the cover after the concrete is placed
• b.Checking the lower mat before the upper mat starts✓
• c.Reading the grade stamp on a bar at the mill
• d.Counting the bar bundles as they arrive on site

A benchmark inspection happens at a stage after which the work is covered or built over, such as the lower mat before the upper mat. Counting bundles is delivery checking, a mill stamp is a material check, and cover after the pour is too late.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 4

Under the federal specification's cover table, what cover applies to #8 bars exposed to weather or ground but not cast against it?

• a.2 inches✓
• b.3/4 inch
• c.1 1/2 inches
• d.3 inches

The table gives 2 inches for bars #6 through #18 exposed to weather or ground. 3/4 inch is for interior surfaces, 1 1/2 inches is for #5 and smaller, and 3 inches is for concrete cast against and permanently in contact with ground.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)

Which is more likely to leave unsatisfactory concrete: under-consolidation or over-consolidation?

• a.Too little vibration, which leaves voids and honeycomb✓
• b.Too much vibration, since it separates the aggregate from paste
• c.Both are about equally likely to cause trouble
• d.Neither one, since vibration changes only the color

Caltrans notes that unsatisfactory concrete is much more likely from too little vibration, which leaves honeycomb, rock pockets and cold joints. Overvibration can separate the mix but is the lesser risk, the two are not equally likely, and vibration affects consolidation, not color.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

Why should an internal vibrator not touch the subgrade when a slab on grade is being consolidated?

• a.It would stir subgrade soil into the concrete✓
• b.It would draw the water out of the fresh concrete
• c.It would short out the motor in the vibrator head
• d.It would wear out the head of the vibrator quickly

Contact with the subgrade disturbs it and incorporates soil into the concrete. Head wear, motor shorting, and water loss are not the stated reason.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

How can bleeding be reduced during placement?

• a.Vibrate a good deal longer at each insertion point
• b.Spray extra water over the surface as it goes in
• c.Place it faster, using a wetter and looser mix
• d.Place slowly with a stiffer mix low down✓

Bleeding can be reduced by slower placement and stiffer concrete, particularly in the lower part of the forms. A wetter mix and more surface water add bleed water, and extra vibration does not cure it.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

What is a cold joint?

• a.A break caused by a delay between lifts✓
• b.A crack caused by freezing weather
• c.A contraction joint sawed after hardening
• d.A construction joint formed with a keyway

A cold joint results from a delay between lifts so that the earlier concrete has begun to set. A sawed joint is a contraction joint, a keyway is a construction-joint detail, and a freeze crack is a different defect.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

A finisher wants to add water to concrete in a chute, or use a vibrator, to keep it flowing. What does Caltrans allow?

• a.A vibrator is allowed but water is not
• b.Water is allowed but a vibrator is not
• c.Neither is allowed✓
• d.Water is allowed if the load has slump to spare

The contractor must not add water to concrete in a chute or use a vibrator to promote its free flow. Spare slump does not permit adding water, and allowing either one alone gets the rule wrong.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

How must placing of a Caltrans element proceed once it has started?

• a.For as long as the finishers keep pace
• b.Stopping and restarting whenever it suits the crew
• c.In stages, with a rest between each truck
• d.Continuously, until the cure is applied✓

Once started, placement must continue without interruption until curing is applied. Planned rests, matching the finishers' pace, and stop-and-go placing invite cold joints.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

What should the inspector keep checking throughout a pour?

• a.Rebar clearances, fixing displaced bars and dobies✓
• b.A running count of cylinders made for the pour
• c.The amount of form oil used on the forms
• d.The slump of the first truck delivered to the site

Clearances of the reinforcing steel are checked throughout the pour, and displaced bars and broken dobies are fixed. A first-truck slump, form oil, and cylinder counts do not cover steel moving during placement.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

In hot weather, what is the easiest and most effective way to lower the temperature of the mix?

• a.Chill the mixing water✓
• b.Add extra cement to the batch
• c.Warm the aggregate stockpile
• d.Paint the truck drums black

Cooling the mixing water, including by using ice, is the easiest and most effective way to cool the mix. Warming aggregate raises the temperature, extra cement adds heat, and black drums absorb heat (white drums absorb less).Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

In cold weather, what is the highest temperature to which water or aggregate may be heated under Caltrans specifications?

• a.90 °F
• b.150 °F✓
• c.212 °F
• d.120 °F

Neither water nor aggregate may be heated above 150 °F. 90 °F is the upper limit for the concrete as placed, 120 °F is not the stated limit, and 212 °F is boiling water, far too hot.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

Why must frozen aggregate be thawed before it goes into the mixer?

• a.It would harden the cement in the drum
• b.It would cut the air content of the mix
• c.It would make the concrete set too slowly
• d.Thawing in the mixer adds too much water✓

Frozen aggregate thawing inside the mixer adds excessive water to the mix. Slow set, lower air content, and hardened cement are not the stated consequence.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

What is the main advantage of a drop chute, also called an elephant trunk?

• a.It lets the concrete free-fall a longer distance
• b.It speeds up the placing rate of the pour
• c.It helps limit segregation✓
• d.It removes the need for vibrating the concrete

A drop chute directs the flow and helps limit segregation. It does not speed placing, vibration is still required, and its purpose is to reduce free fall, not extend it.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

Bleedwater is on a slab surface before floating. What does the federal guide specification say about using dry cement to soak it up?

• a.Sprinkle a light dusting of dry cement to soak it up
• b.No; drag the excess off or absorb it with porous material✓
• c.Cover the wet surface with a thin layer of sand
• d.Work the bleedwater into the surface with the float

Dry cement must not be used to absorb bleedwater, because it makes a weak, uneven surface; the water is dragged off or absorbed by porous material. Dusting dry cement, floating it in, and covering with sand all leave a weak layer.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)

What radius does the federal guide specification call for on an edger used to round slab edges and joints?

• a.3/4 inch
• b.1 inch
• c.1/2 inch
• d.1/8 inch✓

Edges and joints are rounded with an edger having a radius of 1/8 inch. 1/2, 3/4 and 1 inch are larger than the stated radius.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)

What is laitance?

• a.A web of fine map cracks across the slab surface
• b.A thin film of curing compound on top of the slab
• c.A soupy mix of cement, fine sand and water on top✓
• d.A hard, glassy skin left behind by steel troweling

Laitance is the soupy cement, fine sand and water layer that collects when bleed water accumulates on an excessively wet mix. Steel-troweling gloss, map cracking, and curing film are different things.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

A finished slab surface is soft and powdery. Which cause fits Caltrans's description of dusting?

• a.Far too little water added at the batch plant
• b.Contraction joints that were sawed far too early
• c.Poor curing, over-finishing, or high heat or wind✓
• d.Far too much entrained air in a thick slab

Dusting may come from inadequate curing, over-finishing, or exposure to high temperatures or strong winds. Low batch water, early sawing and heavy air entrainment are not the causes given.Caltrans Reinforced Concrete Construction Manual (June 2025), ch. 5

Under the federal guide specification, how deep are contraction joints cut in a 4-in-thick walk with a jointing tool?

• a.2 inches
• b.1/2 inch
• c.3/4 inch
• d.1 inch✓

Joints are cut 1 inch deep or one-fourth of the slab thickness, whichever is deeper; one-fourth of 4 in is 1 in, so 1 inch governs. 1/2 and 3/4 inch are too shallow, and 2 inches is half the thickness.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)

Unless otherwise indicated, how far apart does the federal guide specification space contraction joints in a concrete walk?

• a.Every 5 feet✓
• b.Every 10 feet
• c.Every 2 feet
• d.Every 50 feet

Walks get contraction joints every 5 linear feet. 10 feet is the maximum for curbs, 50 feet is the maximum spacing for walk expansion joints, and 2 feet is not specified.UFGS 03 30 00 Cast-in-Place Concrete (Chg 10, Aug 2025)